Primer for digital printing

Abstract

An aqueous primer composition comprising: (i) a polymer dispersion selected from the group consisting of an acrylic dispersion, a polyester urethane dispersion, or a blend thereof; and (ii) an aminated polymer wherein the aminated polymer is a poly (ethyleneimine), and wherein the poly (ethyleneimine) is present in an amount of 0.5-25% (w / w).

Description

Technical Field

[0001] The present invention provides an aqueous primer composition suitable for digital printing of plastic substrates. The aqueous primer composition of the present invention is particularly suitable for printing on plastic cores of payment cards and financial cards, followed by heat lamination of the printed surface with an additional plastic layer. Advantageously, the resulting plastic laminate has reduced dye leaching.

[0002] The present invention also provides a process for preparing a digitally printed laminate and a laminate prepared by the process. Background Art

[0003] US 11,066,781 (Eastern Tech) relates to a fabric pretreatment solution for inkjet printing comprising greater than 40% (w / w) of a multivalent salt with up to 5% (w / w) of a blocked isocyanate and up to 40% (% w / w) of an aqueous binder which may be a polyurethane dispersion ("PUD"). Such high concentrations of metal salts render these primers unsuitable for the lamination process of the present invention, and furthermore, there is no disclosure of printing via digital electrophotographic printing (such as HP Indigo).

[0004] US 6,761,940 (Hueck Folien) relates to a primer comprising a thermoplastic polymer, which may also contain a crosslinker, without providing any illustrative examples. The thermoplastic polymer of the primer is preferably a copolymer of ethylene and acrylate monomers. Printing via an HP Indigo electrophotographic digital process is involved. US 6,761,940 does not relate to the use of the polymer dispersion according to the present invention together with an aminated polymer crosslinker.

[0005] The HP Indigo process uses so-called "electronic inks" which are essentially dispersions of pigments in a carrier comprising a paraffin solvent and an ethylene copolymer wherein the comonomers are selected from methacrylic acid and acrylic acid. They tend to have poor adhesion to plastic substrates and poor heat resistance. The thermoplastic nature of the ethylene copolymer binder can cause deformation of the print, thereby reducing print quality. The present invention helps overcome these problems; namely, poor adhesion and poor lamination bond strength, while maintaining print quality during high temperature processing of such prints, including the thermal lamination processes encompassed by the present invention. The present invention also overcomes the problem of dye leaching.

[0006] The inks used in the HP Indigo process (commonly referred to in the art as liquid toner inks) contain thermoplastic polymers, such as copolymers of ethylene and methacrylic acid or acrylic acid. The prior art has involved many primers containing such copolymers, which are used for subsequent printing with liquid toners via electrophotographic printing. US 7,470,736 (Michelman) and WO 2020 / 190723 (Sun Chemical) are related to aqueous primer compositions containing ethylene and acrylic acid (or methacrylic acid) copolymers and polyurethane dispersions. Although suitable as print acceptability primers for digital printing, they will not be able to maintain print quality and achieve good lamination bond strength during hot lamination without the additional crosslinking agent present in the primer of the present invention.

[0007] US 9,639,011 (HP) relates to a solvent-based primer for electrophotographic digital printing comprising a copolymer of ethylene and methacrylic acid or acrylic acid. The primer is applied via electrophotographic printing prior to printing with a pigmented liquid toner ("HP Electrink"). There is no discussion of adhesion, print quality retention during thermal lamination, and provision of good thermal bond strength.

[0008] US 10,564,562 (HP) takes this concept further by applying a similar first-down waterborne primer "Digiprime 050" (eg Michelman) prior to digitally applying the primer following the route disclosed in US 9,639,011.

[0009] US 10,851,262 (Sun Chemical) relates to a similar application primer for digital printing, particularly liquid electrophotographic digital printing ('LEP'). The primer comprises a mixture of a polyurethane dispersion and a self-crosslinking acrylic dispersion, which improves the adhesion and blocking resistance of the printed piece to a range of substrates.

[0010] US Pat. No. 10,301,478 (Ashland) relates to a primer coating, in particular for LEP printing, comprising a cationic polyurethane dispersion and a polyoxazoline or N-vinylpyrrolidone copolymer. The use of any crosslinking agent is not disclosed.

[0011] WO 2021 / 011606 (Michelman) relates to an aqueous primer coating comprising a polyvalent metal salt and an amine-containing polymer suitable for digital printing via electrophotographic and inkjet processes. A thermal lamination process according to the present invention is not disclosed.

[0012] In recent years, the use of digital printing technologies such as powder and liquid electrophotographic printing and inkjet printing has grown significantly. Digital printing is now penetrating many markets that have traditionally been served by analog printing processes (flexographic printing, gravure printing, offset printing, screen printing, etc.). These markets include, for example, graphics, packaging, corrugated paper, textiles, ceramics, commercial printing, etc. Some of the benefits associated with digital printing include on-demand printing, personalization, variable data printing, and reduced stored print inventory.

[0013] The "HP Indigo" liquid electrophotographic printing process of Hewlett-Packard has been successfully implemented commercially in a wide range of printing applications, including the printing of labels and narrow web packaging. In this process, a liquid toner image is formed on a photosensitive drum and electrostatically transferred to a heated intermediate blanket before printing on a web or sheet substrate. A description of the technology is provided in US 4,794,651 and US 5,407,771. The printed pieces produced by such liquid toners are generally particularly lacking in adhesion to plastic substrates and may lack physical robustness, so protective overprint lacquers are required in certain applications. In addition, the problem solved by the present invention is that printed pieces produced by such liquid electrophotographic printing may not produce laminates with sufficient bonding strength to enable the laminates to meet technical requirements. Laminated printed pieces produced by liquid electrophotographic printing (such as the "HP Indigo" printing process) are also prone to dye leaching. The primer according to the present invention solves the problem of dye leaching by fixing the dye to the substrate. The problem of dye leaching has not yet been raised in the prior art.

[0014] Citation or identification of any document in this application is not an admission that such document represents prior art to the present invention. Summary of the invention

[0015] The present invention enables the production of plastic laminates which have been printed with a liquid electrophotographic toner and subsequently heat laminated to a second or additional plastic layer without dye leaching from the plastic laminate. The present invention preferably relates to printing the plastic cores of payment and financial cards and then heat laminating the printed surface with an additional plastic layer. Most particularly, the present invention relates to printing the vinyl chloride or vinylidene chloride homopolymers and copolymers comprising the core of a bank card and then heat laminating an additional plastic layer which may also contain vinyl chloride or vinylidene chloride homopolymers and copolymers.

[0016] Thermal lamination is a process in which a second plastic film is brought into contact with the printed surface of the card core and then subjected to elevated temperatures (typically in excess of 100°C, more typically in excess of 120°C) and elevated pressures (typically in excess of 50 bar, and up to 200 bar) to form a bonded laminate. Without the primer of the present invention, not only do card cores printed with liquid electrophotographic fluids lack the necessary lamination bond strength, but also print quality is degraded during thermal lamination and dye leaching. This reduction in print quality is due to ink "migration" during thermal lamination. Likewise, dye leaching is caused by internal dye migration during thermal lamination. The inventors do not wish to be bound by any theory behind this reduction in print quality or dye leaching, but assume that it is due in part to the thermoplastic nature of the polymer binder of the toner which softens and deforms during lamination.

[0017] The primer according to the present invention helps to overcome the defects associated with adhesion and lamination bond strength while maintaining print quality. The primer according to the present invention also prevents dye leaching. This is achieved by using appropriate polymer dispersions and aminated polymer crosslinkers. Again, the inventors do not want to be bound by any theory, but assume that after printing, a portion of the crosslinker migrates from the primer to the ink so that when the printed piece is laminated, both the primer and the ink are crosslinked to maintain print quality. In addition, the inventors assume that after printing, a portion of the crosslinker migrates from the primer to the ink and fixes the dye to the substrate, thereby preventing leaching.

[0018] The prior art does not disclose the use of a printably acceptable primer according to the present invention in the manufacture of payment and financial cards, in particular for electrophotographic (toner) printing. Background Art Many examples in the literature describe primers for electrophotographic printing comprising polymer dispersions but without the necessary crosslinker (poly(ethyleneimine)) that is critical to the process of the present invention.

[0019] Printing acceptable primers for digital printing, particularly electrophotographic printing, having crosslinkers activated during heat lamination have not been disclosed. Without the crosslinker, print quality is degraded during heat lamination for forming finished payment and financial cards, and the inclusion of the crosslinker results in significantly stronger lamination bond strength than without the crosslinker.

[0020] The benefits of printing onto a thermoplastic primer to ensure good print receptivity followed by activation of the curing reaction by the high temperature of hot lamination to ensure that print quality and good lamination bond strength are maintained during the lamination period have not been anticipated in the prior art. Furthermore, there is no disclosure in the prior art of using the primer composition according to the present invention to prevent dye leaching after hot lamination.

[0021] The present invention relates to an aqueous primer composition comprising: (i) a polymer dispersion selected from an acrylic dispersion, a polyester urethane dispersion or a blend thereof; and (ii) an aminated polymer, wherein the aminated polymer is poly(ethyleneimine), and wherein the poly(ethyleneimine) is present in an amount of 0.5-25% (w / w). Preferably, the aqueous primer composition (also referred to as a printably acceptable primer) is applied to a substrate via flexographic printing, gravure printing or screen printing. The primer may then be overprinted with one or more digital inks. Preferably, the overprinting is performed via digital electrophotographic (toner) printing.

[0022] Although primarily directed to aqueous print-acceptable primers for overprinting via digital electrophotographic (toner) printing, the primers of the present invention are also suitable for overprinting via inkjet printing, and are particularly suitable for aqueous inkjet printing inks (i.e., overprinting via inkjet printing with aqueous inkjet printing inks).

[0023] It is described that the aqueous print-acceptable primer according to the present invention comprising poly(ethyleneimine) as a crosslinker is suitable for curing at temperatures above 80° C. after overprinting via an electrophotographic (toner) or inkjet digital printing process. Preferably, the primer is applied by flexographic, gravure or screen printing methods.

[0024] In a preferred application, the primer of the invention is used in the manufacture of payment and financial cards (such as credit cards, bank cards, etc.), wherein the primer is applied to a card core, digitally printed thereon, which is then heat laminated to a second layer and possible further plastic layers. For the manufacture of payment and financial cards, the primer of the invention ensures that the print quality is maintained during the heat lamination process, and also ensures that the bond strength between the primed and digitally printed core and the subsequent plastic layer of the final card is preferably more than 7N after aging for 2 weeks at 55°C and 93% relative humidity. The bond strength can be measured using a JJ Lloyd bond strength tester, and preferably the minimum bond strength is ≥7N / cm, more preferably ≥10N / cm, even more preferably ≥15N / cm, even more preferably ≥17N / cm or most preferably ≥20N / cm. The primer of the invention also prevents dye leaching.

[0025] The problem of dye leaching is solved by using an aqueous primer coating composition comprising a polymer dispersion and poly(ethyleneimine) as an aminated polymer crosslinker. In particular, the problem of dye leaching is solved by using an aqueous primer coating composition comprising a polymer dispersion selected from acrylic dispersions, polyester urethane dispersions and blends thereof and 0.5-25% (w / w) poly(ethyleneimine). After printing, the primer is crosslinked during hot lamination to form the finished card. It is conceivable that some of the crosslinker in the primer will migrate into the ink, so that both will crosslink during lamination. In the absence of a crosslinker, print quality may be reduced and lamination bond strength may be weaker than that achieved when a crosslinker is included. In addition, in the absence of a crosslinker, dyes may leach from the ink.

[0026] The primer of the present invention allows the manufacture of digitally printed payment and financial cards (as well as identification cards). This is very beneficial, allowing the advantages associated with digital printing such as variable data, personalization, printing on demand, and even printing personal security features to be realized. The inventors have shown that the use of a primer according to the present invention is key to ensuring that print quality is maintained and that good lamination bond strength is achieved when the primed and printed core of the card is heat laminated to a further plastic layer at temperatures in excess of 100°C. The use of the primer of the present invention is also key to preventing dye leaching.

[0027] These significant advantages afforded by the present invention allow for digital printed production of payment and financial cards which is not currently possible.

[0028] Furthermore, the present invention enables the market's desired transition from analog to digital printing of such cards.

[0029] The primer according to the invention is first applied to a plastic card core, dried and then digitally printed to produce the desired image and information, the printed core is then heat laminated to additional plastic layers and any other production processes are carried out, such as the inclusion of holograms, etc.

[0030] After coating the substrate (e.g., card core) with the primer of the present invention, overprinting can then be performed by any digital process, including liquid electrophotographic (toner) printing, dry electrophotographic (toner) printing, and inkjet printing. For inkjet printing, the present invention is particularly suitable for printing with aqueous inkjet inks, but also allows printing with UV-curable, energy-curable inkjet inks and solvent-based inkjet inks. However, the present invention is particularly suitable for liquid electrophotographic (toner) printing, such as Hewlett-Packard's "HP Indigo" process.

[0031] The waterborne basecoat according to the present invention comprises a polymer dispersion selected from the group consisting of acrylic dispersions, polyester urethane dispersions (eg, nonionic polyester urethane dispersions) and blends thereof.

[0032] Primer according to the present invention also comprises an aminated polymer cross-linking agent, which is poly(ethyleneimine). Poly(ethyleneimine) can have a straight or branched structure, but a branched structure is preferred. As will be appreciated, poly(ethyleneimine) has amine functional groups on the polymer backbone. In the case where poly(ethyleneimine) is branched, in addition to having amine functional groups on the polymer backbone, it can also have amine functional groups on the side chains. Preferably, poly(ethyleneimine) is branched and has amine functional groups on the polymer backbone and the side chains.

[0033] The primers of the present invention may also optionally contain additional aminated polymers such as poly(vinylamine), copolymers of vinylamine, aminated starches, amine-functional poly(ethylene glycol), amine-functional poly(propylene glycol), and blends thereof.

[0034] A suitable commercially available poly(ethyleneimine) useful in the present invention is Loxanol MI 6735 (BASF).

[0035] The average molecular weight of the poly(ethyleneimine) may be ≥10,000 g / mol, for example, from about 10,000 g / mol to about 50,000 g / mol. Preferably, the average molecular weight of the poly(ethyleneimine) may be from about 20,000 g / mol to about 40,000 g / mol, more preferably from about 20,000 g / mol to about 30,000 g / mol.

[0036] The primer of the present invention may also optionally contain additional crosslinking agents, such as heat-activated blocked isocyanates, polycarbodiimides (e.g., Carbodilite, e.g., Nisshinbo); oxazoline-functional polymer crosslinkers (e.g., Epocros, e.g., Nippon Shokubai); melamine-formaldehyde (e.g., Maprenal, e.g., Ineos Melamines); zinc ammonium carbonate solutions; zinc oxide nanoparticles (e.g., Oxylink, e.g., Buhler).

[0037] The primer of the present invention may also optionally contain a heat-blocked isocyanate. Where used, the heat-blocked isocyanate is preferably present in an amount of 0.5-5% by weight of the primer composition.

[0038] As understood in the art, blocked isocyanates are a class of crosslinking agents in which the reactive isocyanate groups of the crosslinking agent have been reacted with a suitable blocking agent. Thus, a heat-activated blocked isocyanate crosslinking agent is a blocked isocyanate that can be unblocked (i.e., activated) upon heating (e.g., at a temperature above 80°C). Typically, heat-activated blocked isocyanate crosslinking agents are unblocked (i.e., activated) at 90-200°C, preferably 100-180°C. Examples of blocking agents and their typical unblocking temperatures are as follows: diethyl malonate ("DEM"; 100-120°C), 3,5-dimethylpyrazole ("DMP"; 110-120°C), methyl ethyl ketoxime ("MEKO"; 140-160°C), and caprolactam (160-180°C). Such blocked isocyanates, which can be difunctional, trifunctional, tetrafunctional or more functional relative to the number of isocyanate groups per molecule, allow the preparation of stable one-component crosslinkable compositions and are used in many applications, including automotive coatings and textile inks. The blocked isocyanate crosslinking agent used to prepare the primer of the present invention is advantageously water-based. Trixene BI220 (e.g., Lanxess) is used in the preparation of the embodiments. The blocking group used in the preparation of Trixene BI220 is DMP, which allows the deblocking at typical temperatures (such as 120-160° C.) used in the production of payment cards and financial cards thermal lamination. Blocked isocyanates are available from multiple suppliers, including Lanxess ("Trixene"), Covestro ("Imprafix"), Aquaspersions ("Aqualink"), Rudolf GmbH ("Rucopud"), Evonik ("Vestanat") .

[0039] In an alternative embodiment of the present invention, the primer composition is preferably free of additional crosslinking agents such as heat-activated blocked isocyanates, polycarbodiimides, oxazoline functional polymer crosslinkers, melamine-formaldehyde, zinc ammonium carbonate solutions, zinc oxide nanoparticles. For example, in an alternative embodiment, the primer is free of heat-activated blocked isocyanates.

[0040] The primer composition comprises 0.5-25% (w / w), preferably 0.5-20% (w / w), more preferably 0.5-15% (w / w) poly(ethyleneimine).

[0041] The crosslinking agent may comprise 0.5-25%, preferably 0.5-20%, more preferably 0.5-15% of the primer composition on a dry weight basis.

[0042] Preferably, the polymer of the polymer dispersion comprises 2.5-99.5% (w / w) of the primer composition on a dry weight basis; preferably 10.0-98%; more preferably 20.0-95%.

[0043] Preferably, the primer according to the invention comprises a polyester urethane dispersion. Anionic, cationic and nonionic polyester urethane dispersions can be used, but nonionic polyester urethanes are preferred. A suitable commercially available polyester urethane dispersion that can be used in the present invention is NeoRez R-9340 from Cavestro. The polyester urethanes can be aromatic and aliphatic.

[0044] Preferably, the primer composition according to the present invention comprises a polyester urethane dispersion and 0.5% to 25% (w / w) poly(ethyleneimine), preferably 0.5% to 15% (w / w) poly(ethyleneimine), more preferably 0.5% to 8% (w / w) poly(ethyleneimine).

[0045] Alternatively, the primer according to the invention preferably comprises an acrylic dispersion. Anionic, cationic and nonionic acrylic dispersions can be used, but nonionic acrylic dispersions are preferred. A suitable commercially available acrylic dispersion that can be used in the present invention is Alberdingk EP 124181 from Alberdingk-Boley.

[0046] Preferably, the acrylic dispersion is an acrylic homopolymer dispersion. As will be understood in the art, the homopolymer comprises at least 95 mol % of a single monomer unit, preferably at least 98 mol % of a single monomer unit, more preferably at least 99.5 mol % of a single monomer unit. For example, an acrylic homopolymer generally comprises at least 95 mol % of an acrylic monomer, preferably at least 98 mol % of an acrylic monomer, more preferably at least 99.5 mol % of an acrylic monomer. As used herein, unless otherwise indicated, the acrylic monomer constituting the acrylic homopolymer may be acrylic acid or methacrylic acid. For example, an acrylic homopolymer may include a polymer comprising at least 95 mol % of a monomer unit derived from acrylic acid and / or methacrylic acid, but a homopolymer comprising 95 mol % of a monomer unit derived from acrylic acid is preferred. As will be understood in the art, an ethylene acrylic acid copolymer comprising less than 95 mol % of an acrylic acid monomer is not an acrylic acid homopolymer. Preferably, the primer composition according to the present invention does not include any ethylene acrylic acid copolymer (i.e., an ethylene acrylic acid copolymer comprising less than 95 mol % of an acrylic acid monomer).

[0047] Preferably, the primer composition according to the present invention comprises an acrylic dispersion and 0.5% to 25% (w / w) poly(ethyleneimine), preferably 1% to 20% (w / w) poly(ethyleneimine), more preferably 3% to 15% (w / w) poly(ethyleneimine).

[0048] Alternatively, the primer composition according to the present invention preferably comprises an acrylic dispersion and a polyester urethane dispersion.

[0049] Primers according to the present invention may optionally further comprise a polyurethane dispersion ("PUD"), wherein the polyurethane is prepared from a polyether diol, a polyacrylic diol or a polycarbonate. For example, the primer composition may comprise a polyurethane prepared from a polyether diol (i.e., a polyether urethane). A suitable polyether urethane is Rheolate 278 available from Elementis. Where used, the additional polyether urethane is present at 0.01-5% by mass of the primer composition. Typically, the additional polyether urethane is used as a thickener to achieve the desired viscosity.

[0050] Anionic, cationic and nonionically stabilized PUDs as well as aromatic and aliphatic PUDs are all encompassed by the present invention.

[0051] Where the primer composition of the present invention also comprises a PUD prepared from a polyether glycol, polyacrylic glycol or polycarbonate, anionic PUDs may be used, particularly those produced typically by including a carboxylic acid in the polymer structure of the PUD, such as by the urethane reaction of dimethylolpropionic acid ("DVA"). Where DMPA or other acid-containing materials are incorporated into the PUD backbone, neutralization may then be performed with any organic or inorganic base to provide an anionic stabilization mechanism. Where applicable, these various resin types may be neutralized with organic bases including, but not limited to, ammonia, triethanolamine, triisopropanolamine, dimethylaminoethanol, N-methyldiethanolamine or arginine. Alternatively, they may be neutralized by inorganic bases including, but not limited to, alkali metal oxides, alkali metal hydroxides or alkali metal carbonates, sodium hydroxide and potassium hydroxide.

[0052] There are a variety of commercially available PUDs that can be used in the present invention, including those sold under the trademarks Neorez (DSM), Bayhydrol (Covestro), Sancure (Lubrizol), Syntegra (Dow), Luplen (BASF), Beetafin (BIP), Daotan (Allnex), and those PUDs supplied under the "U" nomenclature by Obotex.

[0053] Typically, the polymer dispersion used in the present invention has a solids content of 20-50%, preferably 25-45%.

[0054] The waterborne primer of the present invention may also optionally further comprise any ionic or nonionic styrene-acrylic dispersion. Suitable styrene-(meth)acrylic resin dispersions are widely available commercially and include those sold under the trade names Joncryl (BASF), Revacryl (Synthomer), Hycar (Lubrizol), Neocryl (DSM), Neboplast (Necarbo) and Picassian AC series (Picassian Polymers). It should be understood that this is not a restrictive enumeration, and those skilled in the art will appreciate that any other styrene-(meth)acrylic resin dispersions may be used.

[0055] The waterborne primer of the present invention may also optionally further comprise any solution polymer (also referred to as an alkali-soluble polymer), including alkali-soluble acrylic acid and styrene-acrylic acid polymers. As will be appreciated, alkali-soluble polymers generally refer to polymers that generally comprise an acid moiety as part of a monomer blend, which can be neutralized with a suitable base (including but not limited to ammonia, an amine (e.g., triethylamine or triethanolamine) or an inorganic base (e.g., NaOH, KOH)) to form a polymer that can be dissolved in water to form an aqueous solution. In the case of using alkali-soluble acrylic acid or styrene-acrylic acid polymers, they include any blend comprising acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, and vinyl, acrylic acid or methacrylic acid monomers (including but not limited to styrene, methyl methacrylate, butyl acrylate, butyl methacrylate, ethyl acrylate, ethyl methacrylate, ethyl hexyl acrylate, ethyl hexyl methacrylate). The aqueous solutions of these acrylic acid polymers are formed by neutralizing the carboxylic acid groups of the polymer with any base (including but not limited to ammonia, trimethylamine, triethanolamine, sodium hydroxide, potassium hydroxide) while dissolving the polymer in water.

[0056] The primer according to the present invention may optionally further comprise a polyvalent metal salt. If a polyvalent metal salt is present, it is preferably present in an amount of less than 20% (w / w), more preferably less than 10% (w / w), even more preferably less than 5% (w / w). Suitable polyvalent metal salts include (but are not limited to) polyvalent cation salts, such as calcium nitrate (and its hydrate), calcium ammonium nitrate, calcium acetate and calcium chloride. Preferably, the primer according to the present invention comprises less than 20% (w / w) of calcium nitrate (and its hydrate), calcium ammonium nitrate, calcium acetate or calcium chloride, more preferably less than 10% (w / w) of calcium nitrate (and its hydrate), calcium ammonium nitrate, calcium acetate or calcium chloride, even more preferably less than 5% (w / w) of calcium nitrate (and its hydrate), calcium ammonium nitrate, calcium acetate or calcium chloride.

[0057] Alternatively, the primer according to the present invention is substantially free of polyvalent metal salts, i.e. the primer comprises less than 1% (w / w) of polyvalent metal salts. Thus, in an alternative preferred aspect of the present invention, the primer comprises less than 1% (w / w) of calcium nitrate (and its hydrate), calcium ammonium nitrate, calcium acetate or calcium chloride. In a more preferred alternative aspect of the present invention, the primer does not contain any (i.e. is free of) calcium nitrate, calcium ammonium nitrate, calcium acetate or calcium chloride. Preferably, the primer does not contain any (i.e. is free of) polyvalent metal salts.

[0058] Primer composition according to the present invention comprises water. Advantageously, water does not contain ionic impurities. In one embodiment, water is ion exchanged water or distilled water. In one embodiment, the amount of water used according to the present invention comprises the amount of water supplied as a part of the raw materials used, which will account for 20-80% by mass of the whole composition, preferably 30-70% by mass.

[0059] The primer may also optionally contain any co-solvents including, but not limited to, ethanol, propanol, butanol, acetone, propylene glycol, glycerol, glycol ethers.

[0060] The primer may also optionally contain any number of additives including, but not limited to, surfactants, wetting aids, antifoams, deaerators, biocides. Suitable additives are described herein, but it should be understood that the present invention is not limited to these additives.

[0061] The primer may also optionally contain any dispersion of inorganic materials including, but not limited to, silica, alumina, and clay.

[0062] Preferably, the total solid content of the primer composition is 5.0-60.0% (w / w), more preferably 5.0-40.0% (w / w).

[0063] The primer may be adapted to be applied by any suitable printing or coating method including but not limited to flexographic printing, gravure printing, screen printing, roller coating, spraying. In one embodiment, flexographic printing and screen printing would be the deposition method.

[0064] Because the primer of the present invention is essentially water-based, they can also include biocides or antifungal agents. Suitable examples include products based on the following biocide structure types sold under the trade names Intercide (Akcros Chemicals) or Nipacide (Clariant): benzisothiazolinone, bromonitropropanediol, isothiazolinone, ethylene glycol dihydroxymethyl ether or iodopropynyl butyl carbamate. Other types of biocides that can be considered include sodium dehydroacetate (Geogard 111S from Lonza), sodium benzoate (Vancide 51 from RTVANDERBILT), sodium salt of mercaptopyridine-1-oxide (Sodium Omadine from Arch Chemicals), sodium salt of o-phenylphenol (Dowicide A from Dow Chemical) and ethyl paraben (Nipastat sodium from Aako). These are generally used in amounts of 0.01 to 1.00 mass % of the primer composition.

[0065] Defoamers may also be optionally included in the formulation; these can prevent the formation of foam during primer manufacture and when printing. Defoamers are particularly important for recirculating print heads. Examples of suitable defoamers include TEGO FOAMEX N, FOAMEX 1488, 1495, 3062, 7447, 800, 8030, 805, 8050, 810, 815N, 822, 825, 830, 831, 835, 840, 842, 843, 845, 855, 860 and 883, available from Evonik, TEGO FOAMEX K3, TEGO FOAMEX K7 / K8, and TEGO TWIN 4000. Available from BYK are BYK-066N, 088, 055, 057, 1790, 020, BYK-A 530, 067A and BYK 354. Additives DC62, DC65, DC68, DC71 and DC74 are available from Dow Corning. Agitan 120, 150, 160, 271, 290, 298, 299, 350, 351, 731, 760, 761 and 777 are available from Munzing. Surfynol 104PA, AD01, DF-110, DF-58, DF-62, DF-66, DF-695, DF-70 and MD-20 are available from Air Products.

[0066] Surface control additives may optionally be used to control the surface tension of the primer to produce the desired spreading and wetting on the substrate. They may also be used to control the level of slip and scratch resistance of the coating. Examples of suitable surface control additives include, but are not limited to, TEGO FLOW 300, 370 and 425, TEGO GLIDE 100, 110, 130, 406, 410, 411, 415, 420, 432, 435, 440, 482, A115 and B1484, TEGO GLIDE ZG 400, TEGO RAD 2010, 2011, 2100, 2200N, 2250, 2300, 2500, 2600, 2650 and 2700, TEGO TWIN 4000 and 4100, TEGO WET 240, 250, 260, 265, 270, 280, 500, 505 and 510, and TEGO WET KL245, all of which are available from Evonik. Available from BYK Chemicals are BYK 333 and 337, BYK UV 3500, BYK 378, 347 and 361, BYK UV3530 and 3570, CERAFLOUR 998 and 996, NANOBYK 3601, 3610 and 3650, and CERMAT 258. Available from Cytec are EBECRYL 350 and 1360, MODAFLOW 9200, and EBECRYL 341. Aliphatic silicone acrylate CN9800 from Sartomer can be used. Surfynol 104, 420, 440, 465, 485, 61, 82 and 2502 are available from Air Products. Multiwet BD, EF, SU, SO and VE are available from Croda. DuPont offers Capstone FS-30, 31, 34, 35, 50, 51, 60, 61, 63, 64, 65 and 3100. BASF's nonionic Hydropalat series is also suitable for use.

[0067] Suitable deaerators may optionally be included in the primer to prevent the formation of air inclusions and pinholes in the dried coating that may affect the performance of the primer. Examples include the following products available from Evonik: TEGO AIREX 900, 910, 916, 920, 931, 936, 940, 944, 945, 950, 962, 980 and 986.

[0068] Preferably, the water-based primer of the present invention is colorless. Alternatively, the water-based primer can also include one or more colorants, including pigments and / or dyes. The example of suitable organic or inorganic pigments includes carbon black, zinc oxide, titanium dioxide, phthalocyanine, anthraquinone, perylene, carbazole, monoazo and diazobenzimidazole, rhodamine, indigo, quinacridone, diazopyranthrone, dinitroaniline, pyrazole, diazopyranthrone, pyrazole, dianisidine, pyranthrone, tetrachloroisoindoline, dioxazine, monoazo acrylate (monoazoacrylide) and anthrapyrimidine (anthrapyrimidine). Dye includes but is not limited to azo dyes, anthraquinone dyes, xanthene dyes, azine dyes and combinations thereof.

[0069] Commercially available organic pigments classified according to the International Color Index may be used, including but not limited to those named according to the following trade names: blue pigments PB1, PB15, PB15:1, PB15:2, PB15:3, PB15:4, PB15:6, PB16, PB60; brown pigments PB5, PB23 and PB265; green pigments PG1, PG7, PG10 and PG36; yellow pigments PY3, PY14, PY16, PY17, PY24, PY65, PY73, PY74 PY83, PY95, PY97, PY108, PY109, PY110, PY113, PY128, PY129, PY138, PY139, PY150, PY151, PY154, PY156, PY175, PY180 and PY213; orange pigments PO5, PO15, PO16, PO31, PO34, PO36, PO43, PO48, PO51, PO60, PO61 and PO71; red pigments PR4, PR5, PR7, PR9, PR22, PR23, PR48, PR48:2, PR49, PR112, PR122, PR123, PR149, PR166, PR168, PR170, PR177, PR179, PR190, PR202, PR206, PR207, PR224 and PR254; purple pigments PV19, PV23, PV32, PV37 and PV42; black pigments PBk1, PBk6, PBk7, PBk8, PBk9, PBk10, PBk11, PBk12, PBk13, PBk14, PBk17, PBk18, PBk19, PBk22, PBk23, PBk24, PBk25, PBk26, PBk27, PBk28, PBk29, PBk30, PBk31, PBk32, PBk33, PBk34, PBk35, NBk1, NBk2, NBk3, NBk4, NBk6, and combinations thereof, etc.

[0070] After grinding with a particle size distribution of 10-500nm or 10-350nm, the pigment is ground to less than 1 micron for better transparency and wide color gamut.

[0071] In order to incorporate the above-mentioned pigment into the composition of the present invention, the pigment can be manufactured and stably stored in water as a pigment concentrate. This is usually achieved by using a water-soluble and / or water-dispersible surfactant that introduces hydrophilic functional groups into the surface of the pigment particles to disperse the pigment into a water-soluble or water-dispersible resin. The examples of these dispersed resins are many, and can include polyvinyl alcohol, polyacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylate copolymer, acrylic acid-acrylate copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylate copolymer, styrene-α methyl styrene-acrylic acid copolymer, styrene-α methyl styrene-acrylic acid-acrylate copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl acetate-maleate copolymer, vinyl acetate-crotonic acid copolymer and vinyl acetate-acrylic acid copolymer, and salts thereof. Copolymers can be used in any form of random copolymers, block copolymers, alternating copolymers and graft copolymers. Examples of such resins include Joncryl 67, 678, 8500, 586, 611, 680, 682, 683 and 69 available from BASF. Examples of salts include sodium hydroxide, potassium hydroxide and salts of basic compounds such as ammonia, ethylamine, diethanolamine, triethanolamine, propylamine, isopropylamine, dipropylamine, butylamine, isobutylamine, diethanolammonium, triethanolamine, triisopropanolamine, dimethylethanolamine, aminomethylpropanol and morpholine. The amount of the basic compound is not strictly limited as long as the resin dispersant is equal to or greater than the neutralization equivalent.

[0072] Examples of surfactants used to prepare pigment dispersions include anionic surfactants such as alkane sulfonates, α-olefin sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, acylmethyl taurates, dialkyl sulfosuccinates, alkyl sulfates, sulphurized olefins, polyoxyethylene alkyl ether phosphates, polycarboxylic acids and monoglycerol phosphates; amphoteric surfactants such as alkyl pyridinium salts; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl amides, glycerol alkyl esters and sorbitan alkyl esters. Examples include EFKA 1000, 4000, 5000 and 6000 series products from BASF, Tamol series products from Dow, and Solsperse 27,000, 40,000, 44,000, 46,000 and 47,000 from Lubrizol.

[0073] The primer of the present invention is suitable for application to plastic substrates (such as plastic cards). Suitable plastic substrates (such as plastic cards) include those made of polyvinyl chloride acetate, polyvinyl chloride, polyvinylidene chloride or any blend of these polymers or their copolymers. The substrate is preferably polyvinyl chloride. Preferably, the substrate is a plastic card. The plastic card is suitable for being made of polyvinyl chloride acetate, polyvinyl chloride, polyvinylidene chloride or any blend of these polymers or their copolymers. Therefore, the substrate is preferably a plastic card made of polyvinyl chloride acetate, polyvinyl chloride, polyvinylidene chloride or any blend of these polymers or their copolymers.

[0074] The primer of the present invention is preferably applied to the plastic core of a card, preferably a payment card. The primer of the present invention is applied to the plastic core of the card by any suitable printing or coating method, such as flexographic printing or screen printing. The core of the payment card is typically made of polyvinyl chloride acetate, polyvinyl chloride, polyvinylidene chloride or any blend of these polymers or their copolymers. However, it should be understood that the primer is suitable for coating any plastic core used in the manufacture of payment cards and financial cards.

[0075] Once substrates (eg card cores) have been coated with the primers of the invention, they are then printed via any of the digital printing processes outlined previously. Preferably, the primed cores will be printed via a liquid electrophotographic process such as Hewlett-Packard's "Indigo".

[0076] In one embodiment, the film weight (after drying) of the primer coating applied to the first substrate of the present invention is between 0.1 gm and 10.0 gm. -2 , preferably 0.1-5.0 gm -2 , more preferably 0.2-5.0 gm -2 within the range.

[0077] The printed, primed core is then heat laminated to an additional plastic layer, which may be the same polymer type as the core or a different polymer. This is a process well known to those skilled in the art and typically involves contacting the laminated plastic layer with the printed core and subjecting the plastic layer to a temperature of typically 120-160° C. under pressure, although lower or higher temperatures may be used. Pressures typically in excess of 5 psi, more typically in excess of 10 psi, are used. Heat lamination typically requires anywhere from 0.1 seconds to 30 minutes.

[0078] Without the primer according to the invention, the inventors found that cards produced via Indigo printing were insufficient in lamination bond strength and were susceptible to leaching. The primer provided the final card structure with a lamination bond strength of ≥5 N / cm, ≥7 N / cm, ≥10 N / cm, 15 N / cm or ≥17 N / cm. DETAILED DESCRIPTION

[0079] definition

[0080] Molecular weight - "Molecular weight" or "average molecular weight" refers to the weight average molecular weight (Mw). Molecular weight is suitably measured by techniques known in the art such as gel permeation chromatography. Preferably, molecular weight is measured by comparison with polystyrene standards. For example, molecular weight measurements can be performed on a Hewlett-Packard 1050 series HPLC system equipped with two GPC Ultrastyragel columns (103 and (5 μm mixed, 300 mm×19 mm, Waters Millipore Corporation, Milford, MA, USA) with THF as mobile phase. The skilled person will appreciate that this definition of molecular weight applies to polymeric materials which typically have a distribution of molecular weights.

[0081] Particle size / average particle size - The term "particle size" or "average particle size" refers to the median particle size of the volume distribution (equivalent spherical diameter corresponding to 50% of the volume of all particles, read on a cumulative distribution curve of volume % versus particle diameter - usually referred to as the "D(v,0.5)" value). Particle size is preferably measured by laser diffraction.

[0082] Unless otherwise specified, the term nanoparticle refers to a particle having one dimension less than 100 nm.

[0083] Unless otherwise stated, the lamination bond strength is measured via a T-peel test using a JJ Lloyd tensiometer at a separation speed of 300 mm / min. The lamination bond strength is reported as N / cm, i.e., the force required to separate the top film from the primed and printed core for a 1 cm wide strip; for example, the lamination bond strength reported as N / 25 cm is the force required to separate the top film from the primed and printed core for a 25 cm wide strip. Ideally, the minimum bond strength is ≥5 N / cm, ≥7 N / cm, ≥10 N / cm, ≥15 N / cm, ≥17 N / cm, or ≥20 N / cm.

[0084] Unless otherwise stated, viscosity was measured with a Brookfield CAP200 viscometer equipped with a No. 4 spindle at 50 rpm and at a temperature of 19.1°C.

[0085] Leaching

[0086] Black inks are often tinted with a photo-reflective (basic) blue pigment. This makes dark shades of black more aesthetically appealing when carbon black is tinted with basic blue. However, basic blue is primarily a dye and under certain conditions, when exposed to moisture / heat and / or high relative humidity (e.g. 50°C / 90% RH), such as those of credit card lamination, the blue dye can be seen to leach out of the black ink, causing the black printed image (in the case of HP Indigo) to appear noticeably bluer, which is undesirable. The leaching effect is also evident on fine text, where blue shadows can be seen outlining the black letters, and when delaminated, the laminating adhesive can appear blue due to migration on the basic blue. Examples 1 and 2 of the present invention address this leaching problem by providing dye fixative properties that prevent leaching of the blue dye throughout the printed image.

[0087] Example 1 of the present invention solves the leaching problem with 0.53 wt% poly(ethyleneimine). In contrast, dye leaching is still observed in the case of Reference Example 5 containing only 0.30 wt% poly(ethyleneimine). Therefore, the skilled person will understand that although waterborne primers with less than 0.3 wt% poly(ethyleneimine) provide good lamination bond strength, they do not solve the problem of dye leaching.

[0088] The present invention has been described in detail, including various embodiments thereof. However, it will be appreciated that those skilled in the art, after considering this disclosure, may modify and / or improve the present invention within the scope and spirit of the present invention.

[0089] Example

[0090] The present invention is further described by the following non-limiting examples, which further illustrate the invention and are not intended, nor should they be construed, to limit the scope of the invention.

[0091] Preparation of flexographic and screen printing primers according to the invention

[0092] The primer coating was prepared according to the formulation listed in Table 1. The components were added sequentially, with the polymer dispersion being added first and then blended using a Dispermat high shear mixer.

[0093] Table 1: Examples of primer formulations

[0094]

[0095] 1 Anionic polyurethane dispersion (Obodi; 28% solids); 2Oil-in-water emulsion of ethylene acrylic acid copolymer (Honeywell; 44.5% solids); 3 Nonionic polyester urethane dispersion (40% solids; Covestro); 4 Multifunctional cationic poly(ethyleneimine) crosslinker (BASF); 5 Water-based polymer dispersion (Paramelt; 33% solids); 6 Defoamer (Evonik); 7a,7b Biocides (Thor; 7a 35% solids, 7b 50% solids); 8 Surfactants / wetting additives (Evonik); 9 Polyurethane thickener (Allnex; 37.5% solids); 10 Blocked isocyanate dispersion (LANXESS; 41% solids); 11 Carbodiimide crosslinker (Nisshinbo Co., Ltd.; 40% solids); 12 Anionic dispersions of PU polyols, such as Evonik (33% solids); 13 Polyurethane-based thickener (25% solids); 14 Non-anionic acrylic dispersion (40% solids; Opdi Corporation).

[0096] The viscosity (poise) was measured using a Brookfield CAP200 viscometer (spindle No. 4, 50 rpm, 19.1°C).

[0097] Embodiment description:

[0098] Reference Example 1: Flexographic printing PUD primer formulation containing blocked isocyanate dispersion crosslinker.

[0099] Reference Example 2: Screen printing PUD primer formulation containing blocked isocyanate dispersion crosslinker.

[0100] Reference Example 3: PUD primer formulation containing an oil-in-water emulsion of ethylene acrylic acid copolymer, a blocked isocyanate dispersion crosslinker, and a carbodiimide crosslinker.

[0101] Reference Example 4: PUD primer formulation containing an oil-in-water emulsion of ethylene acrylic acid copolymer, a blocked isocyanate dispersion crosslinker and an anionic dispersion of PU polyol.

[0102] Inventive Example 1: Screen printing polyester urethane primer formulation containing 0.53 wt% of a multifunctional cationic polyethyleneimine crosslinker with improved leaching resistance.

[0103] Inventive Example 2: Screen printing acrylic primer formulation containing a multifunctional cationic polyethyleneimine crosslinker with improved leaching resistance.

[0104] Reference Example 5: Screen printing polyester polyurethane primer formulation containing 0.3 wt % of a multifunctional cationic polyethyleneimine crosslinker.

[0105] The primer composition was applied to a PVC-based payment card core at 12 gsm (wet) and then dried to achieve a dry film weight in the range of 2.5 to 3.5 gsm (dry). The primed PVC core was then printed with a liquid electrophotographic ink via an HP Indigo sheet-fed printer. The primed and printed core was then heat laminated to a second flexible PVC film under various conditions according to Table 2. The lamination bond strength was measured via a T-peel test using a JJ Lloyd tensiometer at a separation speed of 300 mm / min; this is a test type familiar to those skilled in the art. The lamination bond strength is reported as N / cm; this is the force required to separate the top PVC film from the primed and printed core for a 1 cm wide strip.

[0106] Adhesion was measured by tape test using 3M Scotch magic tape. According to ASTM F2252 / 52252M-13 (2018), it was placed on the surface of the printed substrate and rolled 5 times with a 2 kg roller. The ink removal rate was then recorded as %. All embodiments of the present invention passed the tape test, indicating good adhesion.

[0107] It was observed that in the absence of any primer, the transfer of ink to the vinyl core was poor and the adhesion assessed by the tape test was also poor.

[0108] Table 2: Primer performance characteristics

[0109]

[0110] The results in Table 2 show that the primer of the present invention provides an improvement in lamination bond strength compared to the absence of the primer. As shown in the results in Table 3, Examples 1 and 2 of the present invention also prevented the leaching of the basic blue dye from the indigo black ink.

[0111] Table 3: Leaching evaluation

[0112]

[0113] Test Methods for Leaching Evaluation

[0114] HP indigo ink and basic blue dye were diluted with Isopar at a 2:1 ratio (2 parts black ink: 1 part Isopar) and printed using a 40 micron k-bar, which deposited a wet coating weight of approximately 40 gsm on a portion of the HP EPDM image transfer blanket.

[0115] Once coated, the rubber was transferred to a hot plate at 160°C until all the solvent evaporated, leaving only the ink as a film layer. The blanket was then placed with the ink side down on a pre-primed PVC substrate and a 2kg hand ink roller was used to press the surface several times. The prints were then allowed to cool completely before further testing.

[0116] Lamination: The ink was printed onto a pre-primed substrate and allowed to cool completely. The area printed with black ink was cut into strips and laminated to a PVC cover using a heat sealer (140°C / 40psi / 20 seconds). The strips were then cut into 25 mm strips and divided into multiple sections, one of which was placed into a humidity controlled oven (50°C / 90% RH / 7 days) and the remaining samples were left in a controlled dark environment. Visual and color measurements were taken on the humidity aged samples and those stored in a controlled environment.

[0117] X-Rite (obtain LAB and ΔLAB results) Method: The color change of the sample is measured using an X-Rite spectrometer, which measures the following parameters to give a numerical value indicating the color change, where:

[0118] ΔE is a standard measurement that uses a combination of dL*, da*, and db* to quantify the difference between two colors.

[0119] ΔE is measured on a scale of 0 to 100, where values ​​≤ 1.0 are generally imperceptible to the human eye. Values ​​of 1.0-2.0 are perceptible with careful observation. Values ​​between 2.0-10 are obvious at a glance. Values ​​in the range of 11-49 are clearly different colors. Values ​​>49 are considered to be the opposite.

[0120] dL* represents the lightness / darkness difference between two measurements.

[0121] The samples that exhibited less leaching had lower ΔE(DEcmc) and ΔL values ​​compared to the samples where leaching was observed.

[0122] Visual Color Evaluation: Samples aged in a humidity controlled oven (as described above) were visually compared to unaged samples and evaluated. No color change was a pass; a slight visual color change was a marginal pass; a significant visual color change was considered a fail.

[0123] Table 3 shows the improvements in lower measured color change values ​​and reduced visual color change for Examples 1 and 2 of the present invention. Thus, Examples 1 and 2 are particularly suitable for applications where reduced leaching is desired.

Claims

1. A waterborne primer composition comprising: (i) a polymer dispersion selected from an acrylic dispersion, a polyester urethane dispersion, or a blend thereof; and (ii) an aminated polymer, wherein the aminated polymer is poly(ethyleneimine), and wherein the poly(ethyleneimine) is present in an amount of 0.5-25% (w / w).

2. The primer composition of claim 1 wherein the polymer dispersion is a polyester urethane dispersion and the aminated polymer is poly(ethyleneimine).

3. The primer composition of claim 1 wherein the polymer dispersion is an acrylic dispersion and the aminated polymer is poly(ethyleneimine).

4. A primer composition according to any one of the preceding claims, wherein the polymer dispersion comprises more than 40% (w / w) of the total composition.

5. A primer composition according to any one of the preceding claims, comprising 0.5-20% (w / w) of the aminated polymer, preferably 0.5-15% (w / w) of the aminated polymer.

6. The primer composition of any of the preceding claims, wherein the poly(ethyleneimine) has a molecular weight of about 10,000 g / mol to about 50,000 g / mol.

7. A primer composition according to any one of the preceding claims, wherein the polymer of the dispersion comprises 2.5-99.5% of the primer composition on a dry weight basis, preferably 10.0-98% of the primer composition, more preferably 20.0-95% of the primer composition.

8. A primer composition according to any one of the preceding claims, wherein the total solids content of the primer composition is 5.0-60.0% (w / w), more preferably 5.0-40.0% (w / w).

9. A primer composition according to any one of the preceding claims, wherein the composition is substantially free of multivalent metal salts (ie the composition comprises less than 1% w / w multivalent metal salts).

10. A primer composition according to any one of the preceding claims, wherein the composition comprises less than 1% (w / w) calcium nitrate, calcium ammonium nitrate, calcium acetate, calcium chloride or a blend thereof, preferably wherein the composition comprises less than 0.5% (w / w) calcium nitrate, calcium ammonium nitrate, calcium acetate, calcium chloride or a blend thereof.

11. A primer composition according to any one of the preceding claims, wherein the composition does not contain any calcium nitrate, calcium ammonium nitrate, calcium acetate or calcium chloride.

12. A primer composition according to any one of the preceding claims, wherein the composition comprises 20-80% water by mass of the composition, preferably 30-70% water by mass of the composition.

13. A method of providing a primed substrate comprising applying a primer composition according to any one or more of claims 1 to 12 and drying the primer.

14. The method of claim 13, wherein the substrate is polyvinyl chloride (PVC).

15. The method according to claim 13 or 14, wherein the primer is applied to the substrate by flexographic printing, gravure printing or screen printing.

16. A method of providing a primed and printed substrate comprising applying a primer composition according to any one or more of claims 1 to 12 and drying the primer, thereafter printing one or more inks on top of the primer and drying the subsequent one or more inks.

17. The method of claim 16, wherein the substrate is polyvinyl chloride (PVC).

18. The method according to claim 16 or 17, wherein the primer is applied to the substrate by flexographic printing, gravure printing or screen printing.

19. The method according to claim 16, 17 or 18, wherein the one or more inks are printed on the primed substrate by digital printing, preferably by liquid electrophotographic (Indigo) printing, dry electrophotographic (toner) printing or inkjet printing.

20. The method according to any one or more of claims 13 to 19, wherein the primed and printed substrate is heat laminated with one or more further plastic layers.

21. The method according to claim 20, wherein: Said hot lamination of the further plastic layer is carried out at ≥ 80°C, preferably ≥ 100°C.

22. A method for preparing a laminate structure, comprising the steps of: a. applying the primer composition according to any one of claims 1 to 12 to a first substrate; b. drying the primer; c. overprinting the primed substrate with one or more digital inks; d. drying the one or more digital inks; and e. Laminating the second substrate to the primed and printed first substrate at ≥ 80°C to produce a laminate structure.

23. The method according to claim 22, wherein the lamination is performed at ≥ 100°C.

24. A laminate structure prepared according to the method of claim 22 or 23.

25. The laminate structure of claim 24 which is a plastic payment card.

26. Use of an aqueous primer composition as defined in any one of claims 1 to 12 for reducing dye leaching in a laminate structure.

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